Efficient high-resolution wake modeling using the vorticity transport equation

Computational fluid dynamic models, through their fundamental treatment of the flow physics, present a unique and powerful tool for analyzing the aerodynamics of helicopter rotors. Their effectiveness is often limited though by difficulties in retaining the structure and form of the rotor wake that result from their tendency to dissipate vorticity. The vorticity transport model, developed some years ago, addresses the problem of vorticity diffusion by solving the fundamental fluid dynamic equations in vorticity conservation form. A development of the original model is described that results in a more efficient computational implementation. The new model uses an adaptive grid system to increase grid resolution significantly, with minimal impact on computational cost. The new grid system is effectively boundary free, thus eliminating the need for numerical boundary conditions at the edges of the computational domain. In addition, the new grid system allows very efficient evaluation of the velocity field using a technique based on the Cartesian fast multipole method. The implementation of both the grid system and the velocity calculation is described, and the performance of the new model is validated against some well-known experimental data.